The present invention is directed to an inference system applied to plant control.
FIG. 4 is a block diagram illustrating a configuration of a conventional production system reported, e.g., on p. 49 of [Expert System Introduction Actual Practice Guide] (Oct. 4, 1988), published by Denki Shoin.
The production system includes a knowledge base unit 1 for storing a knowledge base defined as a set of rules. Connected to the knowledge base unit 1 is a working memory 2 conceived as a region for temporarily storing an intermediate hypothesis to be modified (the modification implies rewriting and adding) and executed on the rules of the knowledge base. Connected to the knowledge base unit 1 and the working memory 2 is an inference engine 3 for applying the rules in accordance with contents of the working memory 2 from the rules of the knowledge base.
The following is a description of the operation.
A rule employed for the inference is selected from those stored in the knowledge base unit 1.
In the production system, the working memory 2 for temporarily storing the intermediate hypothesis obtained in the course of inference exhibits a present status.
The contents of the working memory 2 are matched with conditions written to a condition part of the rule stored in the knowledge base unit 1. If all the conditions coincide with the contents of the working memory 2, the rule is selected as an applicable one.
If a plurality of rules is selected, one of these rules is further selected.
The one rule selected therefrom is fired, and then a procedure written to an action part is executed.
The contents of the working memory 2 are thus rewritable.
Thereafter, this cycle is repeated. When no single piece of applicable rule is left, or when executing a termination command written to the action part of the fired rule, the inference comes to an end.
The conventional inference system is configured in the way described above. Where the number of objects for inference is 1, the system is effective. In the case of plant control to which the system is actually applied, there exists a multiplicity (several hundreds or even several thousands) of motors or valves of one kind as objects. For this reason, if the system is applied directly to the plant control, the configuration is exemplified by FIG. 5. The knowledge base unit 1 and the working memories 2 remarkably increase in quantity. This requires the use of a large amount of computer memory. Besides, during an execution of inference of one object, the inference of other remaining objects is not allowed to be executed till matching with all the rules of the knowledge base is finished. The plant control under which on-line inference is required presents such a problem that a detection of fault is delayed.
Accordingly, it is an object of the present invention, which has been devised to obviate the foregoing problems, to provide an inference system capable of effecting on-line inference of all objects without causing any delay of a fault detection.